This invention relates in general to devices used in the manufacture of electromagnetic coils and in particular to an improved apparatus for passing an electrical current through a wound electromagnetic coil so as to perform a resistance bonding operation.
The electromagnetic coil is a well known device which is adapted to generate a magnetic field when an electrical current is passed therethrough. Such coils are typically formed by winding an insulated copper wire about a central form. The central form may be a core formed from iron or a similar electrically conductive material, or it may be a spool formed from plastic or a similar non-conductive material. In both of these types of coils, the central form becomes an integral part of the finished coil. In other coils, however, the wire is wound about a mandrel which is subsequently removed. Thus, a free standing coil having a central opening is provided.
Regardless of whether the coil is provided with an integral conductive core or non-conductive spool, or whether it is free standing, it is often desirable to subject the coil to a resistance bonding operation. The resistance bonding operation increases the strength and rigidity of the coil and prevents the wire from unwinding. As mentioned above, the wire is covered by an electrical insulating material. However, in wire used for resistance bonded coils, the electrical insulating material is itself covered by a coating of a bonding material. The resistance bonding operation is designed to increase the temperature of the bonding material such that the adjacent windings of the wire are bonded together. To accomplish this, the ends of the wound wire are connected to a source of electrical power so that electrical current passes therethrough. The resistance of the wire to the passage of this current generates heat in the wire. The heat melts the coating of the bonding material on the wire without affecting the integrity of the insulating material.
In the past, the resistance bonding operation has been performed by an operator on an open fixture. The operator manually clamped the ends of the wire to respective terminals, then closed a pair of hand switches (spaced apart from the fixture for safety) so as to connect the terminals to the source of electrical power. Normally, the resistance bonding operation lasts only for a few seconds. However, during that period of time, an electromagnetic field is generated by the coil. The operator, who is located relatively close to the coil during the resistance bonding operation, is thus exposed to this electromagnetic field. Although such exposure is not known to create any health hazards for the operator, it would be desirable to provide an improved fixture which reduces or eliminates this exposure, and which permits the resistance bonding operation to be performed more quickly and reliably.